The effects of adaptation to compounds representative of the four basic taste qualities on the transient response of single hamster chorda tympani fibers will be studied. Several stimulus compounds, selected on the basis of their taste quality to man, will be presented following each adapting stimulus and after distilled water. The cross adaptation effects will be analyzed in two ways: (1) according to the across-fiber pattern view of quality coding, and (2) according to the "labelled-line" hypothesis. Given that adaptation to a basic compound blocks that particular sensation quality in man, comparison of these electrophysiological results with the human psychophysical data on the effects of cross adaptation may reveal the nature of gustatory quality code. Similar work will be initiated on neurons at the levels of the nucleus tractus solitarius and thalamus of the hamster.